Sometimes you just need a hammer!
And I mean a real one - not a warhammer or Mjølnir. Just something that gets the job done. For my sheet metal project I needed a small dead blow hammer.
What is a dead blow hammer, you might ask: A dead blow hammer lets you controll your strike force, minimizes the damage to the target and has almost no rebound effect.
Print everything in PLA or PETG with 4 walls and 40% infill. For the head faces you can use PLA as well but I used TPU because I wanted a softer impact. You can print the head faces with both materials and exchange them whenever needed as they will be screwed-on. Supports are not necessary.
Glue the handle to the shaft and the shaft to the neck. Make sure you seal all gaps by using a gap filling glue (e.g. Uhu Endfest 300). Screw one head face to the neck then fill the neck to 3/4 with sand or salt or sugar or steel balls or depleted uranium - whatever you have at hand (I used ~50g quartz sand). The heavier the better. At last screw-on the second head face.